Hemoglobin biosynthesis involves three separate processes, initiation, elongation, and termination. Our research is concerned with the enzymatic mechanisms of the various steps of the elongation process. Two of these steps, the binding of aminoacyl-tRNA and translocation, appear to involve the hydrolysis of GTP although this stoichiometry has not been unequivocally established in mammalian systems. In order to optimally study these steps and the mechanisms involved the reticulocyte ribosomes must be washed extensively to remove elongation factors and other proteins. The treatment results in the inactivation of a large percentage of the ribosomes. We have devised a method employing poly U:Sepharose affinity chromatography for separating the active ribosomes of such a preparation from the inactive ones. Much of our present work involves the characterization and stabilization of such active ribosomes. The ribosomes may prove to be advantageous in studying the details of GTP hydrolysis, hopefully negating the large amount of nonspecific background hydrolysis seen in other studies of this type. This work also involves the further purification and characterization of the reticulocyte elongation factor, EF-2, which is involved in translocation.